1. Field of the Invention
The present invention relates to a polishing pad for use in chemical mechanical polishing.
2. Description of the Related Art
The chemical mechanical polishing (CMP) is a procedure for planarizing the surface of a substrate with a polishing pad. The CMP is generally applied in polishing lens, mirrors, substrates of liquid crystal displays, silicon wafers, and oxidation and/or metal layers on silicon wafers.
Taking silicon wafers as an example, ingots of monocrystalline silicon are sliced first. The wafers are usually lapped to make them flat for subsequently chemical etching. A polishing process is required after the etching process. During the polishing process, a polishing pad together with slurry reacts chemically with the silicon atoms on the surface of the wafer to make the reacted surface softer than the underlying silicon. Furthermore, the reacted surface is continually wiped away, causing fresh silicon to be exposed to the slurry and the polishing pad.
A conventional polishing pad comprises a base material comprising fibers. A polishing layer comprising a porous elastomer such as polyurethane is also provided on or in the base material. By using a pressure sensitive adhesive (PSA), the conventional polishing pads are secured to a polishing platen or head of a polishing machine. The pressure sensitive adhesive comprises a carrier film comprising polyester, for example, and has an adhesive with a low fluidity on an upper side and a lower side of the carrier film. Such an adhesive is known as the dual-sided adhesive. The adhesive on the upper side of the carrier film is configured to couple the base material of the polishing pad, and that on the lower side of the carrier film is to couple the polishing platen or head of the polishing machine.
Because the base material of the polishing pad comprises fibers, contents of the base material are not distributed evenly. The variations of the thickness of the base material are easily observed. Besides, the surface of the base material is not flat and is usually rough and undulant. Such features make the base material difficult to attach tightly and completely to the carry film of the PSA. On the other hand, the polishing platen or head of the polishing machine usually has a flat surface. It follows that the adhesion strength between the base material and the carrier film is weaker than that between the carrier film and the polishing platen or head of the polishing machine. Therefore, the polishing pad easily detaches from the polishing machine. Additionally, when the polishing pad is replaced, residues of the PSA are easily left behind on the polishing platen or head and the residues of the PSA need to be removed and the time needed for replacing polishing pad is lengthened. Furthermore, a thickness of the carrier film of about 0.1 mm is too thin, and a folding line easily occurs. On the other hand, the pH resistance of the conventional adhesive is not satisfactory. The effect and efficiency of the CMP are both reduced thereby.